1. Field of Invention
The present invention relates to a method of fabricating capacitors. More particularly, the present invention relates to a method of fabricating cylindrical capacitors.
2. Description of Related Art
Cylindrical capacitors are now widely used in dynamic random access memories that have memory capacity greater than 256M. FIGS. 1A through 1C are a series of diagrams showing the progression of manufacturing steps in fabricating a cylindrical capacitor over a device using a conventional method.
First, as shown in FIG. 1A, a shallow trench isolation (STI) structure 102, a gate oxide layer 104 and a gate 106 are formed above a substrate 100. Source/drain regions 108 are also formed in the substrate 100 one each side of the gate 106. Thereafter, an oxide layer 110, which serves as an insulating layer, is formed over the substrate 100. Then, a contact opening 112 is formed in the oxide layer 110 so that one of the source/drain regions 108 can be electrically connected by subsequent deposition of a conductive material.
Next, as shown in FIG. 1B, a second conductive layer 114 is formed over the oxide layer 110. Then, the conductive layer 114 is patterned to form a recessed opening 116 using photolithographic and etching operations. The recessed opening 116 is formed inside the conductive layer 114 above the contact opening 112. However, the recessed opening 116 does not penetrate the conductive layer 114 to expose the contact opening 112 or the oxide layer 110. Subsequently, the conductive layer 114 is patterned again forming a conductive layer 114a as shown in FIG. 1C. The cylindrical conductive layer 114a and the conductive material inside the contact opening 112 together form the lower electrode of the capacitor. Finally, a dielectric layer 116 and a third conductive layer 118 are sequentially formed over the conductive layer 114a, wherein the conductive layer 118 functions as the upper electrode of the capacitor.
In the conventional method of fabricating cylindrical capacitors, photolithographic and etching operations have to be carried out twice. Hence, processing is more complicated and consistent product quality is more difficult to achieve. In addition, dimensions of capacitor structures are difficult to control using conventional photoresist patterning techniques.
In light of the foregoing, there is a need to improve the method of fabricating cylindrical capacitors for memory devices.